what has always annoyed me is now ready to be asked on this list. :)
It appears like apt-get/aptitude/dpkg dealing with the list/database of
installed packages is terribly slow at times. I have roughly 1800 packages
installed and it sometimes takes 20-30 seconds to install a single
package

I've experienced this myself, so much that I'm about to change my
perfectly working IDE disk for a SATA disk with the intent of fixing
this.
On my attempts to fix this, I changed some of the HD parameters, and
it improved a bit, but not completely.
My only guess about why this happens is that at some point the
hard-drive was a bit too-full, so that it started to become
fragmented, and the package db never de-fragmented, even if I later
emptied the disk. This is just a wild guess. It might be something
completely different.
--
Besos,
Marga